Phyllomanganates are ubiquitous in a variety of environments and commonly enriched in transition metal elements, such as Ni. The effect of such foreign metal cations on phyllomanganate transformation is widely documented under aqueous conditions together with the induced modification of Ni geochemical behavior. A similar knowledge is lacking however on phyllomanganate transformation and on the induced fate of associated metal elements that may occur under dry conditions, that prevail in deserts and arid areas increasingly exposed to severe droughts or wildfires. The present study shows that crystallinity, morphology, Mn oxidation state, and Ni binding mechanisms are essentially unaffected when aging hexagonal birnessite (Mn oxidation state ∼ 3.90 and Ni/Mn molar ratios of 0.00 and 0.13) in the dry state at room temperature for up to 8 years. In contrast, heating aged Ni-doped birnessite to 25–200 °C results in an increased proportion of edge-sharing Ni-Ni(Mn) pairs with increasing temperature induced by the migration of interlayer Ni to birnessite octahedral layers and/or by an increased sharing of coordination oxygens by interlayer Ni/Mn from adjacent layers. Further heating to 400 °C does not change this proportion, with birnessite layer structure being retained. Transformation of Ni-doped birnessite to cryptomelane is complete at 500 °C, while that of Ni-free birnessite is achieved at 400 °C, suggesting that Ni doping increases birnessite thermal stability. Birnessite-to-cryptomelane transformation comes with a strong increase of Mn oxidation state, whereas this parameter remains unchanged in heated birnessite samples. Ni incorporation in the cryptomelane framework, reduces its release during reductive acid dissolution by a factor of 396 ± 15 compared to initial birnessite. These results shed light on mineral transformation affecting layered manganates under dry conditions and on the fate of associated transition metal elements.

叶锰酸盐在各种环境中普遍存在，并且通常富含过渡金属元素，例如 Ni。这种外来金属阳离子对叶锰酸盐转化的影响在水性条件下被广泛记录，同时也引起了镍地球化学行为的改变。然而，关于叶锰酸盐转化以及可能在干旱条件下发生的伴生金属元素的诱导命运缺乏类似的知识，这种情况在越来越多地遭受严重干旱或野火的沙漠和干旱地区普遍存在。本研究表明，在室温干燥状态下时效六方水钠锰矿（Mn 氧化态 ∼ 3.90 和 Ni/Mn 摩尔比分别为 0.00 和 0.13）时，结晶度、形貌、Mn 氧化态和 Ni 结合机制基本上不受影响到 8 年。相比之下，将老化的 Ni 掺杂水钠锰矿加热到 25-200 °C 会导致随着温度升高，层间 Ni 迁移到水钠锰矿八面体层和/或通过来自相邻层的层间Ni / Mn增加了配位氧的共享。进一步加热到 400 °C 不会改变这个比例，水钠锰矿层结构被保留。Ni掺杂水钠锰矿向隐黑锰矿的转变在500°C时完成，而不含Ni的水钠锰矿在400°C时完成，这表明Ni掺杂提高了水钠锰矿的热稳定性。水钠锰矿到隐晶石的转变伴随着锰氧化态的强烈增加，而该参数在加热的水钠锰矿样品中保持不变。Ni并入cryptomelane框架，与初始水钠锰矿相比，还原性酸溶解过程中的释放量减少了 396 ± 15 倍。这些结果揭示了在干燥条件下影响层状锰酸盐的矿物转化以及相关过渡金属元素的命运。